The present invention relates generally to a thermal treatment furnace and, more particularly, to a thermal treatment furnace having a function of preventing a gas in the furnace from leaking to the outside. The term xe2x80x9cthermal treatmentxe2x80x9d used in this specification widely means that an object is heated for treatment in a gas atmosphere, and includes the case where a chemical reaction such as oxidation or reduction takes place.
FIG. 1 illustrates a cross-sectional view of a conventional thermal treatment furnace. A thermal treatment furnace 10 includes a reaction tube 1 and a cap 2. The cap 2 closes an opening 3 of the tube 1 to confine a gas in the tube 1. The tube 1 has a supply port 4 and an exhaust port 5 for a reaction gas. The reaction gas goes to the supply port 4 from a gas supply apparatus (not shown) through a pipe, and is supplied into the tube 1. The gas going out through the exhaust port 5 is treated by a gas treatment apparatus (not shown) and is exhausted. Within the tube 1 are mounted objects 6, for example, semiconductor substrates such as silicon wafers. The interior of the tube 1 is heated by a heater (not shown) provided inside or outside the tube 1.
FIG. 2 is an enlarged view of the portion of a conventional thermal treatment furnace indicated by symbol A in FIG. 1. In the case where the treatment temperature increases to a high temperature of about 800xc2x0 C. or higher, an O-ring for sealing cannot be used at a joint portion between the tube 1 and the cap 2. This is because the heat resistance of the O-ring is low. Therefore, as shown in FIG. 2, a small gap 7 is undesirably produced at the joint portion between the tube 1 and the cap 2, and a problem arises in that the gas in tube 1 leaks through this gap (reference numeral 7 in FIG. 2). Especially when the leaking gas is a highly reactive (corrosive) gas, it has a greatly adverse influence on an external environment. Therefore, a thermal treatment furnace without gas leakage during high-temperature thermal treatment is demanded.
An object of the present invention is to provide a thermal treatment furnace without gas leakage even at the time of high-temperature thermal treatment.
A thermal treatment furnace in accordance with the present invention is characterized by having a reaction tube provided with an opening at one end thereof and a flange surrounding the opening, and a cap abutting on the reaction tube at the flange to close the opening, and including means for preventing a gas in the reaction tube from leaking to the outside through a gap formed at the joint portion between the flange and the cap and further including means for discharging a leaking gas in the gap between joint surfaces of the flange and the cap.
Also, the thermal treatment furnace in accordance with the present invention is characterized in that the flange of the reaction tube constituting the thermal treatment furnace has a groove and a hole for supplying an inert gas into the gap between the joint surfaces of the flange and the cap, and that the flange further has a groove and a hole for discharging the leaking gas passing through the gap between the joint surfaces of the flange and the cap.
The novel features believed to be characteristic of this invention are set forth in the appended claims. The invention itself, however, as well as other objects and advantages thereof, may be best understood by reference to the following detailed description of an illustrated preferred embodiment to be read in conjunction with the accompanying drawings.